Geckos

Golden-tailed Gecko, Strophurus taenicauda.The Robust Velvet Gecko, Oedura robusta, a common house gecko in some outer areas of Brisbane.The Chameleon Gecko, Carphodactylus laevis, from the rainforests of north Queensland.Geckos are a familiar sight to those who live in the tropical regions of Australia. A number of species are common ‘house geckos’, scuttling across our walls and ceilings in pursuit of insects. These animals are a remarkably diverse group and have a broad distribution through tropical and warm temperate regions of the world. A few species can survive in very harsh, cold conditions. One such gecko from New Zealand, Hoplodactylus kahutarae, inhabits rocky bluffs at altitudes of 1300 metres and is active at temperatures as low as 7° C.

Australian geckos belong to the families Diplodactylidae, Carphodactylidae and Gekkonidae. Geckos are easily recognised, being mostly nocturnal with soft bodies and tiny granular scales. They have well-developed limbs with five digits, large eyes with vertical pupils, no eyelids, and broad fleshy tongues. In the absence of eyelids, the tongue is used to lick the eye clean.

There is usually a cluster of enlarged tubercules on either side near the base of the tail. Many species have pores beneath the hind limbs or in the area between the hind limbs (preanal pores) and males typically have a prominent bulge behind the anal area.

Many species have expanded toe pads that provide adhesion and allow them to run on vertical or slippery surfaces (for example, Gehyra spp., Hemidactylus spp. and Oedura spp.), some can run across glass. Other geckos have narrow, bird-like feet for clinging to trees or rocks (for example, Cyrtodactylus spp., Orraya occultus and Saltuarius spp.). Geckos generally lay two eggs per clutch.

During the day, geckos can be found hiding in confined spaces: spider holes, beneath dead bark, in clumps of spinifex, rock crevices and the like.

Most are insect-eaters but sap and nectar are often included in their diets. Some of the larger species will even eat other vertebrates. In the Cooktown area, Cyrtodactylus tuberculatus has been seen eating frogs and other geckos. Australian geckos favour drier habitats and relatively few species occur in rainforest (Carphodactylus laevis, Orraya occultus, Phyllurus spp., Saltuarius spp. are some rainforest inhabitants).

The diversity in Australian geckos is remarkable. There are boldly patterned species (for example, Oedura marmorata and Strophurus taenicauda), drab species (for example, Gehyra dubia and Heteronotia binoei) and some, like the leaf-tailed geckos (Orraya occultus, Phyllurus spp., Saltuarius spp.), with cryptic patterns and broken outlines that blend perfectly with their backgrounds. Some are smooth and others are covered with small, raised tubercules.

The spiny-tailed geckos (Strophurus spp.) have rows of spine-like projections on their tails and eyelids and can squirt a thick, treacly fluid from glands along the back of their tails. The knob-tailed geckos have a small kidney-shaped projection on the end of a disproportionally short tail (Nephrurus spp. - the name means kidney-tail). There is even a species that produces loud squeaking noises from its discarded tail (the Chameleon Gecko, Carphodactylus laevis).

In Queensland, there are 60 recognised species of native gecko and one foreign invader (the Asian House Gecko, Hemidactylus frenatus). However, recent genetic studies point to the Australian gecko fauna as being vastly richer than currently perceived. Undoubtedly more species will be recognised as this work continues.